How does mac os open multiple cap packets?

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Wireshark does not support having multiple capture files open in the same process, so it can't fully function as a standard macOS application.

If Wireshark is installed in /Applications/Wireshark.app, and you have a small shell script called, for example, "wsopen":

#! /bin/sh
/Applications/Wireshark.app/Contents/MacOS/Wireshark "$@"&

in your $PATH, you could open multiple files from the command line with wsopen {file path}. (If there were a Launch Services command-line tool to find the path of an app, that could be made to use the installed path even if it isn't /Applications/Wireshark.app.)

You can open multiple copies of Wireshark from a terminal window with the command: open -n -a /Applications/Wireshark.app.

Unfortunately I don't know of a way to open multiple copies by opening pcaps from the finder.